RT8456 ? ds8456-05 april 2013 www.richtek.com 1 ? copyright 2013 richtek technology corporation. all rights reserved. is a registered trademark of ric htek technology corporation. ordering information note : richtek products are : ` rohs compliant and compatible with the current require- ments of ipc/jedec j-std-020. ` suitable for use in snpb or pb-free soldering processes. marking information pin configurations (top view) sot-23-6 isolated secondary side led lighting current controller features z z z z z secondary side led current regulation z z z z z 4.75v to 48v operation range z z z z z high accuracy 59mv led current threshold control z z z z z 0.6ma operating current z z z z z programmable led current z z z z z output over voltage protection z z z z z small sot-23-6 package z z z z z rohs compliant and halogen free applications z isolated led lighting fixtures z e27/gu10/t5/t8 general description the RT8456 is an isolated secondary led current controller designed specifically for lighting fixtures such as e27, gu10, t5 and t8. the ic is suitable for applications that require power line isolation for safety and reliability, high conversion efficiency, as well as high led current accuracy. the RT8456 contains 1) a constant current regulating amplifier with 59mv threshold used to program the led string current with a simple resistor to within 5% led current accuracy; 2) an over voltage comparator to protect the output when led string is open or broken; 3) and an opto-coupler driver to control the primary side of the transformer to complete the system loop. the RT8456 is offered in a small sot-23-6 package. em= : product code dnn : date code em=dnn cn gnd ovp vcc out cp 4 23 5 6 RT8456 package type e : sot-23-6 lead plating system g : green (halogen free and pb free)
RT8456 2 ds8456-05 april 2013 www.richtek.com ? copyright 2013 richtek technology corporation. all rights reserved. is a registered trademark of ric htek technology corporation. functional pin description pin no. pin name pin function 1 cn non-inverting input of the cc regulating amp. it has a 59mv offset from the cp pin. the cn pin should be connected to the "current in" node of the current sensing resistor, r sense . 2 gnd ground of the RT8456 and secondary side. 3 ovp output over voltage protection pin with threshold of 2.5v. 4 cp inverting input of the cc regulating amp. it has a ? 59mv offset from cn pin. cp pin connects to a resistor to set led current. 5 out open-collector output. connects this pin to an opto-coupler with a current limiting resistor. 6 vcc supply voltage input. a 0.1 f bypass capacitor should be connected between vcc and gnd. function block and typical application circuit vcc gnd RT8456 cp out cn ovp + - + - 2.5v cv cc optocoupler vout led string 59mv r sense r2 r ic1 c ic1 r led r vc1 c vc1 r1 c vcc d1 secondary side winding r cn
RT8456 3 ds8456-05 april 2013 www.richtek.com ? copyright 2013 richtek technology corporation. all rights reserved. is a registered trademark of ric htek technology corporation. recommended operating conditions (note 4) z supply input voltage, vcc (note5) --------------------------------------------------------------------------------- 4.75v to 4 8v z junction temperature range --------------------------------------------------------------------------------------------- ? 40 c to 125 c absolute maximum ratings (note 1) z supply input v oltage, vcc ----------------------------------------------------------------------------------------------- ? 0.3v to 52v z cp ----------------------------------------------------------------------------------------------------------------------------- - ? 0.6v to 1v z cn ----------------------------------------------------------------------------------------------------------------------------- - ? 0.3v to 1v z out ---------------------------------------------------------------------------------------------------------------------------- ? 0.3v to 52v z power dissipation, p d @ t a = 25 c sot-23-6 ------------------------------------------------------------------------------------------------------------------- - 0.4w z package thermal resistance (note 2) sot-23-6, ja ---------------------------------------------------------------------------------------------------------------- 250 c/w z lead temperature (soldering, 10 sec.) -------------------------------------------------------------------------------- 260 c z junction temperature ------------------------------------------------------------------------------------------------------ 150 c z storage temperature range --------------------------------------------------------------------------------------------- ? 65 c to 150 c z esd susceptibility (note 3) hbm (human body model) ----------------------------------------------------------------------------------------------- 2kv mm (ma chine model) ------------------------------------------------------------------------------------------------------ 200v electrical characteristics (v cc = 12v, t a = 25 c, unless otherwise specified) note 1. stresses beyond those listed ? absolute maximum ratings ? may cause permanent damage to the device. these are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. exposure to absolute maximum rating conditions may affect device reliability. note 2. ja is measured at t a = 25 c on a low effective thermal conductivity single-layer test board per jedec 51-3. note 3. devices are esd sensitive. handling precaution is recommended. note 4. the device is not guaranteed to function outside its operating conditions. note 5. RT8456 starts regulation at v cc 4.5v, and meets all parameter specs at v cc 4.75v. parameter symbol test conditions min typ max unit quiescent current i cc v cn = v cp = 0v -- 550 -- a gnd pin current i gnd v cn = v cp = 0v, gnd = 0v -- 530 -- a v cn = v cp = 0v 2.46 2.5 2.54 ovp voltage v ovp v cn = v cp = 0v, t a = ? 25c to 105c 2.45 -- 2.55 v ovp input bias current i ov p v ovp = 2.4 to 2.6v -- -- 100 na v ovp = 2.4v 56 59 62 led current sensing amplifier threshold v cn ? cp v ovp = 2.4v, t a = ? 25c to 105c 55 -- 63 mv cn input bias current i cn -- -- 200 na out maximum pin sink current i outh v out = 1.5v -- 8 -- ma
RT8456 4 ds8456-05 april 2013 www.richtek.com ? copyright 2013 richtek technology corporation. all rights reserved. is a registered trademark of ric htek technology corporation. typical operating characteristics i ovp vs. temperature 0 5 10 15 20 25 30 35 40 45 50 -50 -25 0 25 50 75 100 125 temperature (c) i ovp (na) v cc = 45v v cc = 36v v cc = 12v v cc = 4.75v i cc vs. temperature 400 440 480 520 560 600 640 680 -50 -25 0 25 50 75 100 125 temperature (c) i cc (a) v cc = 45v v cc = 36v v cc = 12v v cc = 4.75v v ovp vs. temperature 2.46 2.47 2.48 2.49 2.50 2.51 2.52 -50 -25 0 25 50 75 100 125 temperature (c) v ovp (v) v cc = 45v v cc = 36v v cc = 12v v cc = 4.75v v outl vs. temperature 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 -50 -25 0 25 50 75 100 125 temperature (c) v outl (v) v cc = 45v v cc = 36v v cc = 12v v cc = 4.75v i out = 2ma i outh vs. temperature 0 1 2 3 4 5 6 7 8 9 10 -50 -25 0 25 50 75 100 125 temperature (c) i outh (ma) v cc = 45v v cc = 36v v cc = 12v v cc = 4.75v v cn-cp vs. temperature 54 55 56 57 58 59 60 61 -50 -25 0 25 50 75 100 125 temperature (c) v cn-cp (mv) v cc = 45v v cc = 36v v cc = 12v v cc = 4.75v
RT8456 5 ds8456-05 april 2013 www.richtek.com ? copyright 2013 richtek technology corporation. all rights reserved. is a registered trademark of ric htek technology corporation. application information output voltage setting the voltage control loop is controlled via the first trans- conductance operational amplifier. an optocoupler which is directly connected to the output and an external resistor bridge is connected between the output positive line and the ground reference. the middle point is to be connected to the ovp pin of the RT8456, where r2 is the upper resistor and r1 the lower resistor of the bridge. the relationship between r2 and r1 is shown below () () out ovp out ovp ovp r1 + r2 v = v x r2 v - v r1 = r2 x v where v out is the desired maximum output voltage. to avoid discharge of the load, the resistor bridge r1, r2, should be highly resistive. for this type of application a total value of 100k (or more) would be appropriate for the resistors r1 and r2. as an example, with r1 = 80k and r2 = 20k , v out = 12.5v output current setting the current control loop is controlled via the second transconductance operational amplifier. an optocoupler and the sense resistor, r sense , is placed in series on the output negative line. v cn ? cp threshold is achieved externally by a resistor bridge tied to the reference voltage, v ref . its middle point is tied to the positive input of the current control operational amplifier and its foot is connected to the lower potential point of the sense resistor. the resistors of the bridge are matched to provide the best precision. with v cn ? cp and r sense , the expected output current, i out, can be obtained as below equation : cn cp out sense v i = r ? where i out is the desired maximum output current, and v cn ? cp the threshold voltage for the current control loop. note that the sense resistor, r sense, should be chosen taking into account its maximum power dissipation (p lim ) during full load operation. compensation both the voltage control trans conductance amplifier and the current control trans-conductance amplifier can be fully compensated. the output and negative inputs are directly accessible for external compensation components, as shown in the typical application circuit. the typical component values for the compensation network of voltage control loop is c vc1 = 2.2nf and r vc1 = 22k . the typical component values for the compensation network of current control loop is c ic1 = 2.2nf, r ic1 = 22k and r cn = 1k . however, in many application conditions, the current control loop can be stable without compensation network (r cn = 0, no c ic1 nor r ic1 ). when the voltage control loop is used as the voltage limit protection or the current control loop is used as the current limit protection, no compensation network is needed for the protecting control loop. a resister, r opt , must be connected in series with the opto-coupler since it is part of the compensation network. although the value of r opt is not critical, it's recommended to be in the range from 0.33k to (v out ? 2) / (0.005) . thermal considerations for continuous operation, do not exceed absolute maximum junction temperature. the maximum power dissipation depends on the thermal resistance of the ic package, pcb layout, rate of surrounding airflow, and difference between junction and ambient temperature. the maximum power dissipation can be calculated by the following formula : p d(max) = (t j(max) ? t a ) / ja where t j(max) is the maximum junction temperature, t a is the ambient temperature, and ja is the junction to ambient thermal resistance.
RT8456 6 ds8456-05 april 2013 www.richtek.com ? copyright 2013 richtek technology corporation. all rights reserved. is a registered trademark of ric htek technology corporation. for recommended operating condition specifications, the maximum junction temperature is 125 c. the junction to ambient thermal resistance, ja , is layout dependent. for sot-23-6 packages, the thermal resistance, ja , is 250 c/ w on a standard jedec 51-3 single-layer thermal test board. the maximum power dissipation at t a = 25 c can be calculated by the following formula : p d(max) = (125 c ? 25 c) / (250 c/w) = 0.4w for sot-23-6 package the maximum power dissipation depends on the operating ambient temperature for fixed t j(max) and thermal resistance, ja . the derating curve in figure 1 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. figure 1. derating curve of maximum power dissipation layout consideration for the best performance of the RT8456, the following pcb layout guidelines must be strictly followed. ` place the r sense resistor as close to the ic as possible. ` keep the input/output traces as wide and short as possible. figure 2. pcb layout guide 0.0 0.1 0.2 0.3 0.4 0.5 0 25 50 75 100 125 ambient temperature (c) maximum power dissipation (w) 1 single-layer pcb v out r vc1 r led c vc1 r1 r2 optocoupler cn gnd ovp vcc out cp 4 23 5 6 led string : : : r sense r ic1 c ic1 d1 secondary side winding c vcc cn r cn
RT8456 7 ds8456-05 april 2013 www.richtek.com richtek technology corporation 5f, no. 20, taiyuen street, chupei city hsinchu, taiwan, r.o.c. tel: (8863)5526789 richtek products are sold by description only. richtek reserves the right to change the circuitry and/or specifications without notice at any time. customers should obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. richtek cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a richtek product. information furnish ed by richtek is believed to be accurate and reliable. however, no responsibility is assumed by richtek or its subsidiaries for its use; nor for any infringeme nts of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of r ichtek or its subsidiaries. outline dimension a a1 e b b d c h l sot-23-6 surface mount package dimensions in millimeters dimensions in inches symbol min max min max a 0.889 1.295 0.031 0.051 a1 0.000 0.152 0.000 0.006 b 1.397 1.803 0.055 0.071 b 0.250 0.560 0.010 0.022 c 2.591 2.997 0.102 0.118 d 2.692 3.099 0.106 0.122 e 0.838 1.041 0.033 0.041 h 0.080 0.254 0.003 0.010 l 0.300 0.610 0.012 0.024
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